Using ghost racing to prepare for the real thing
iRacing offers a neat feature commonly referred to as "ghost mode" that's unfortunately not very well-documented or publicized -- "ghost mode" gives you the ability take a "test drive" during spectator sessions, which allows you to actually race on the track along side the actual competitors as a "ghost car" that racers in the session cannot see or otherwise interact with. You'll be on-track, your car physics will be exactly the same as in any other iRacing session, and you can even benefit from aerodynamic tow from the actual competitors, but they cannot interact with you, and they will literally pass right through you, because as a "ghost" collisions with other cars are not possible. You will also not be risking any iRating or Safety Rating (iR or SR), so this makes for a great way to run practice starts or even full races.
Details on "ghost mode" are sparse, but you can find this covered in Section 3.5 of the iRacing User Guide:
• Spectator Sessions – This link will take you to a page where you can see all the series currently active and be able to join the series as a spectator. You can also drive a ghost car that races in the session cannot see.
All you have to do to use this feature is to join a Spectator Session from the main menu, then select "Test Drive" from the top menu once you enter Spectator Mode.
Your car will start from the pits, but you'll be a "ghost car" that nobody else can see or interact with. Again, no iR or SR applies, so you can just drive with no fear of messing anybody else (or yourself) up. This is a great confidence-builder, and it's a great way to learn your way around a new track -- and even better, if you join a race session you can actually use this method to practice race starts.